fix(dify): accept a bare string for the retrieval response query field

[wahllllll]

AgentScope-Java Version

2.1.0-SNAPSHOT

Description

Fixes #1917

DifyResponse models the top-level query field of a knowledge base retrieval response as an object ({"content": "..."}), which is what self-hosted Dify returns. Dify Cloud (api.dify.ai) returns a bare string for the same field:

{"query": "ping", "records": [ { "segment": { ... }, "score": 0.9 } ]}

Jackson cannot bind a JSON string to DifyResponse.Query, so DifyRAGClient.retrieve throws JsonException: Failed to deserialize JSON to ...DifyResponse and every record is discarded: kb_search returns nothing against Dify Cloud, while stub responses shaped as an object hide the problem.

• Add DifyQueryDeserializer, which maps both "query": "..." and "query": {"content": "..."} to DifyResponse.Query.
• The field is informational -- the Dify integration never reads it (the only callers of DifyResponse#getQuery are the tests added here) -- so a shape that is neither a string nor an object yields a null query instead of failing the response. Losing the query text is harmless; losing all records is not.
• DifyResponse.Query, getQuery()/setQuery() and the self-hosted shape are unchanged, so this is not a breaking change.
• Document both shapes in the DifyResponse and DifyDocumentConverter javadoc.

Validation on commit 9797487:

• Reproduced the reported failure offline first: a MockWebServer response carrying the Dify Cloud payload makes testParseResponseWithBareStringQuery fail on the parent commit with MismatchedInputException: Cannot construct instance of DifyResponse$Query ... from String value ('What is RAG?') -- the same Failed to deserialize JSON to ...DifyResponse error reported in [Bug] Dify Cloud 检索接口 query 字段返回字符串，导致 DifyResponse 反序列化失败（kb_search 对 api.dify.ai 引用恒为空） #1917.
• After the fix, DifyRAGClientTest: 26 passed, 0 failures, 0 errors. The new tests cover the bare-string shape, the object shape (regression guard) and record parsing for both.
• Dify module suite (Dify*Test, RerankConfigTest, RetrievalModeTest): 64 tests run, 0 failures, 0 errors, 0 skipped; Maven reactor for the module and its dependencies: BUILD SUCCESS, Spotless check included.
• No Dify Cloud credentials are available here, so the fix is validated against the payload captured in [Bug] Dify Cloud 检索接口 query 字段返回字符串，导致 DifyResponse 反序列化失败（kb_search 对 api.dify.ai 引用恒为空） #1917 rather than a live call. Accepting both shapes is safe either way: hosts that already work are unaffected.

Checklist

• Code has been formatted with mvn spotless:apply
• All tests are passing (mvn test) -- the affected module and its dependencies passed locally
• Javadoc comments are complete and follow project conventions
• Related documentation has been updated -- no Dify response-shape documentation exists under docs/, so none was changed
• Code is ready for review

[codecov]

Codecov Report

❌ Patch coverage is 64.28571% with 5 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
.../integration/dify/model/DifyQueryDeserializer.java	64.28%	2 Missing and 3 partials ⚠️

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